One of my favorite "secret menu" features of Universe. Pairs nicely with the iOS photos app background removal, too! If you want a button that isn't so "square," try this:
Go to your camera roll + select a picture
Long press on the main part of the picture until you see a little shine run over the selected area (this may take a few tries, but you'll also feel a little rumble when you get it)
Choose 'Share' on the little menu that shows up
Choose 'Save Image'
Add an image block to your site, and select the new, background-less image you created
Under Style, choose "Fit Whole Image"
Follow the steps in this post starting at step #2 to turn it into a linkable button!